This invention relates to an electromagnetic coupling device which is used as a solenoid clutch for transmitting a turning torque or a solenoid brake for braking the turning torque. More particularly, the present invention relates to an electromagnetic coupling device having a built-in electric component for preventing damage of an electric circuit due to a surge voltage, breakage of a V belt when a rotary member on the output side is locked, and the like.
Friction type electromagnetic coupling devices in general, such as solenoid clutches, transmit or cut off the turning torque by passing the magnetic flux generated by the excitation of an excitation coil between a rotor and an armature disposed in such a manner that their friction surfaces are opposed to each other, and bringing the friction surfaces into and out of pressure contact with and from each other by the magnetic attraction and the repulsion of a flexible member against the magnetic attraction.
Among such electromagnetic coupling devices, a solenoid clutch fitted to a refrigeration compressor of an automobile, for example, has a different lead length depending on the kind or model of automobile. Therefore, one kind of yoke having a built-in excitation coil cannot be used as a common automobile component for a variety of automobiles, and this is disadvantageous from the aspects of design and stock management. Therefore, various electromagnetic coupling devices where the excitation coil is connected to the lead wire on the power source side outside the yoke by changing the design of the prior art structure, wherein the excitation coil and the lead wire on the power side are connected outside the yoke, have been proposed in the past (for example, Japanese Laid-Open Nos. 12108/1988 and 125322/1992 (corresponding to U.S. Pat. No. 5,138,293).
In the electromagnetic coupling devices of this kind, a large surge voltage develops across both ends of the excitation coil as soon as the supply of power to the excitation coil is cut off and causes damage of the contacts of a switch or an erroneous operation. Therefore, a diode is connected in parallel with the excitation coil so as to absorb the surge voltage by this diode (Japanese Utility Model Laid-Open No. 12732/1985 and Japanese Patent Laid-Open No. 125322/1992, for example).
The electromagnetic coupling device described in Japanese Patent Laid-Open No. 125322/1992 (hereinafter referred to as the "prior art invention 1") was proposed by the same applicant of the present invention. In this electromagnetic coupling device, a terminal accommodation section is formed integrally with a coil bobbin for accommodating an excitation coil, a winding start portion and a winding end portion of the excitation coil are led into this terminal accommodation section, and a diode is connected in parallel with the excitation coil. The winding start portion and the winding end portion of the excitation coil are forced into the slits of two fitting metals disposed inside the terminal accommodation section, and by partly removing the insulating coating and the two end portions are electrically connected to these fitting metals, respectively. A bent plate of a support metal is forced into each fitting metal and is electrically connected thereto, so that the excitation coil and the diode are connected in parallel.
In the electromagnetic coupling devices of this kind, if the rotary member on the output side does not rotate for some reason or other, heat generation occurs due to the slip between the friction surface of the rotor and the armature, and the V-belt stretched on the rotor is cut. Therefore, the rotor and the armature must be separated from each other by detecting heat generation as soon as possible and by cutting off the supply of power to the excitation coil. Japanese Patent Laid-Open No. 138529/1981 (hereinafter referred to as the "prior art invention 2") and Japanese Patent Laid-Open No. 51025/1982 (hereinafter referred to as the "prior art invention 3"), for example, propose an electromagnetic coupling device using a temperature fuse. In other words, in the solenoid clutch disclosed in the prior art invention 2, a notch is made in an outer peripheral edge of one of the flanges of a coil bobbin having the excitation coil wound thereon, and the winding start portion and the winding end portion of the excitation coil are led out from this notch. A notch is similarly made in the outside end of the other flange, an intermediate portion of the excitation coil is led out so as to form a deflection portion, the deflection portion is then cut and is used as fuse connection terminal sections, and the terminals of the temperature fuse are connected to these terminal sections by pressure-connection terminals so as to connect the temperature fuse in series with the excitation coil. This temperature fuse is fixed by a hook disposed on the other flange.
In the electromagnetic clutch disclosed in the prior art invention 3, a fuse holder section for holding the temperature fuse is formed on the outside surface of a coil bobbin for accommodating the excitation coil and this coil bobbin together with the temperature fuse is molded with a synthetic resin and is insulated from outside.
As described above, if the temperature fuse is connected to the excitation coil, the temperature fuse is fused by the heat generated by the slip between the rotor and the armature, so that the supply of power to the excitation coil can be cut off and breakage of the V-belt, etc, can be prevented in advance.
However, the prior art inventions 1, 2 and 3 described above involve the following problems. In other words, in the electromagnetic coupling device described in the prior art invention 1, the winding start portion and the winding end portion of the excitation coil are inserted through the slit of each fitting metal and electrically connected, each lead of the diode is connected in advance to the lead on the power source side and to the ground wire from the excitation coil by the support metal, and the bent portion of this support metal is forced into the fitting metal so as to electrically connect the support metal and the fitting metal, as described above. Therefore, two metal members of two kinds, that is, the support metals and the fitting metals, or four metal members in all, must be prepared. Therefore, the number of components is large, and the connection work of the excitation coil, the lead wire and the diode is troublesome and time-consuming, and the terminal accommodation section becomes great in size.
In the solenoid clutch described in the prior art invention 2, the excitation coil and the leads of the temperature fuse are connected in advance by the pressure-connection terminals and the fuse is clamped and fixed by the hook. Therefore, this prior art invention 2 involves the problem that the connection work of the temperature fuse and the excitation coil is troublesome and time-consuming.
In the solenoid clutch described in the prior art invention 3, the coil bobbin together with the temperature fuse is molded with synthetic resin. Therefore, it is necessary to inject the molten molding resin into the coil receiving groove of the yoke accommodating the coil bobbin and to cure the resin. Therefore, it takes a long time for the molding, and the productivity drops.